The invention relates to a diversity antenna in the metric and decimetric wave ranges for motor vehicles.
The invention is a multi-antenna system of the type used for providing an antenna diversity system. Such multi-antenna systems are described in European Patent EP 0 269 723, German Patents DE 37 19 692 and 36 19 704, and U.S. Pat. Nos. 4,914,446 and 5,801,663 which employ different types of antennas such as rod aerials, windshield pane antennas or the like. When there is adequate decoupling of the antennas in terms of high frequency, reception interference occurs as the motor vehicle moves through different locations in the field of reception. This reception interference takes results from temporary fading of the reception level because of the multi-way propagation of the electromagnetic waves. The function of an antenna diversity system is to switch from one antenna to another when reception interference occurs in the signal of the operating antenna, as well as to minimize signal loss (or level fading) on the receiver input leading to reception interference within a defined field of reception.
According to the prior art, four antenna amplifiers are used for receiving VHF radio signals. The antenna amplifiers are installed on the edge of a rear window glass pane. The wiring of such antenna amplifiers requires substantial expenditure, which is frequently viewed as intricate in the automaking industry as well.
Signal loss or level fading plotted over the driving distance, and over time occurs incongruently. The likelihood of having an undisturbed signal among the available antennas increases with the number of available antennas and with decoupling between the signals of the antennas in terms of diversity. Decoupling of the antenna signals in terms of diversity exists when the reception signals are different particularly in view of reception interference such as, fading of the HF signal level.
An object of the invention is to design an improved. diversity antenna for a diversity antenna system in a motor vehicle. The antennas receive signals which can be selected in different ways with only one antenna connection, whereby the average reception quality is as good as possible and the reception interference occurring simultaneously in the various antenna signals while the vehicle is moving is similarly low as with separated antennas.
The present invention is in part based on European Patent EP 0 269 723. The use of at least two antennas is required for obtaining antenna signals that are decoupled in terms of diversity. These antennas have to be created from the heating field of a motor vehicle. It is necessary to provide each antenna for a connection network with an antenna amplifier to obtain good signal/noise ratios. These connection networks require a great expenditure, especially in conjunction with the required high-frequency connection lines.